they look indeed like MS Word temp files, to find out what's locking them, you may use this:
LockHunter is a foolproof file unlocker.
It is a tool to delete files
blocked by something you do not know.
LockHunter is useful for fighting
against malware, and other programs
that are blocking files without a
reason. Unlike other similar tools
it deletes files into the recycle bin
so you may restore them if deleted by
mistake.
Key Features
Shows processes locking a file or
folder
Allows to unlock, delete, copy or
rename a locked file
Allows to kill locking process
Allows to remove locking processes
from hard drive
Integrates in to Explorer menu
It deletes files into the recycle bin,
so you may restore them if deleted by
mistake
Supports both 32 and 64bit Windows
LockHunter is freeware.